Vibrational spectroscopy is considered to be the most powerful technique for probing molecular structure, composition, and phase of materials. Its applicability to the study of boundary layer lubrication and other phenomena where materials contact surfaces at high temperature and pressure in elastohydrodynamic (EHD) contact regions, however, has been greatly reduced due to the inaccessibility of the region of interest to infrared radiation. Thus, only a limited amount of information is available concerning what roles high pressure and temperature play in the formation of boundary layers, and concerning how a given lubrication system will perform in a chosen application. The chemical details of boundary lubrication, which are necessary for the development of new and potentially superior lubricant additives, then, are only sparsely available.
IR and Raman spectroscopy have generally been limited to determining chemical changes in absorbed species before and after wear. See, e.g., "Utilization of Raman Spectroscopy in Tribochemistry Studies," by N. T. McDevitt et al., Wear 166, 65 (1993), and "Real-Time Raman Detection Of Molecular Changes In Ceramics Undergoing Sliding Friction," by G. J. Exarhos and M. S. Donley, Microbeam Analysis, pp. 125-127 (San Francisco Press, Inc., 1987).
Diamond anvil cells have long been used to aid in the study of materials under extreme conditions similar to those found in extreme pressure lubrication. Lauer et al., in "Analysis of Infrared Spectra of Fluid Films in Simulated EHD Contacts," J. Lubrication Technology, pp. 145-150 (April 1975), describe the use of interferometric techniques to observe infrared absorption and emission spectra having excellent resolution from small EHD contact regions, in order to determine phase and structural changes in fluids subjected to conditions prevailing in EHD contacts. Contact simulation was believed to be achieved in the cavity of a high-pressure diamond anvil cell. However, the standard Merrill-Bassett type diamond anvil cells employed (See, e.g., "Miniature Diamond Anvil Pressure Cell for Single Crystal X-Ray Diffraction Studies," by Leo Merrill and William Basset, Rev. Sci. Instrum. 45, 290 (1974)) do not provide a metal surface upon which boundary lubrication films can form.
In "Infrared Emission Spectra of Elastohydrodynamic Contacts," by J. L. Lauer and M. E. Peterkin, J. Lubrication Technol., pp. 230-235 (April 1976), and in "Temperature Gradients Through EHD Films and Molecular Alignment Evidenced By Infrared Spectroscopy," by V. W. King and J. L. Lauer, J. Lubrication Technol. 103, 65 (January 1981), the authors describe the observation of infrared emission spectra from thin films of a test fluid located between a diamond disk mounted as a window in a steel plate and a weighted, steel ball which was rotated over the window so as to form a sliding EHD contact region. Some of the radiant energy generated from small areas of this region, both in the fluid and at the boundaries, passes through the diamond window into an infrared interferometer, giving rise to an infrared spectrum. The spectrum may be separated into contributions from the fluid and from the ball surface, making it possible, by appropriate calibrations, to estimate their temperature separately under operating conditions.
Accordingly, it is an object of the present invention to provide a diamond anvil cell which permits the investigation of boundary layer type films under conditions similar to those found in extreme pressure lubrication, and which may be used with spectroscopic techniques including IR absorption, Raman scattering, uv-visible absorption, and fluorescence.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.